My last gig had an MSSQL database component that pushed $700,000 a year.
It wasn't _that_ big but it was pushing the upper published limits of what you could do with an MSSQL RDS. One day replication stopped working, and amazon business support of whatever couldn't resolve it.
I've been around the block and have continuously come to the conclusion that it's usually better to have the skills to run them yourself, and then it's just a balance of whether or not you're time or cash poor.